The Molecular Profiling and Characterization Core is the heart of the UIUC Neuroproteomics Center on Cell-Cell Signaling. Understanding the role of brain chemistry in health, pain management, drug addiction, and withdrawal requires knowledge of the molecules within the brain and their associated neurochemical pathways. The large assortment of chemical messengers and the diversity of their chemical and physical properties require a complex suite of measurement techniques and integrated approaches for dissecting the molecular components of cell-to- cell communication. Mass spectrometry (MS) is a central technique for precise molecular profiling and characterization of complex neurological systems. The primary mission of the Molecular Profiling and Characterization Core is to augment our understanding of addiction-associated processes using MS-based analytics to provide qualitative, quantitative, and functional data on the molecular drivers involved in cell-cell signaling. Positioned between the Sampling and Separation Core and Bioinformatics, Data Analytics and Predictive Modeling Core, this core executes defined studies with maximal data quality and provides tailored MS methods for enabling user-specific experiments that lie at or near current technological limits. We have the outstanding analytical capabilities and well-documented expertise to effectively probe diverse signaling components within tissues, individual cells, and their extracts and releasates with spatial and temporal resolution. These measurements capitalize on the careful study design and rigorous execution by professional staff capable of developing and implementing validated methods across the Center. Between the University of Illinois at Urbana-Champaign and Northwestern University, we are well-equipped with an extensive suite of high- resolution, tandem mass spectrometers and sampling capabilities that are suitable for imaging and molecular analysis of neuropeptides, metabolites, proteins, and protein complexes across a wide molecular-weight range. For proteomics, defined study designs are categorized as ?Bottom-Up? and ?Middle-Down? shotgun approaches in which proteins are digested to various extents prior to MS analysis, and the ?Top-Down? approach in which the intact proteins or whole protein complexes are introduced into the mass spectrometer for structural characterization by tandem MS. We exploit the complementarity of these approaches within the context of specific Center-supported research projects to maximize the molecular specificity and coverage for identification and quantitation of proteins and their post-translational modifications. Future studies will benefit from high- resolution information on relative and absolute amounts of bioactive neuropeptide and metabolite levels obtained in either targeted or discovery modes of operation. We also employ MS imaging approaches to illuminate the ?hidden? peptidome and metabolome to elucidate key molecules and pathways involved in drug abuse and inform treatments for associated conditions such as drug addiction and withdrawal.